Review: “Success weight” and “BoP” (Part 1)

In addition to the difference of the class itself between GT500 and GT300, there are over 40 different car models competing in SUPER GT. Engine power (horsepower), shape of the car, and tires are different, and the performance is uneven, but there are always intense and close battles on the track. This is realized because SUPER GT’s unique rules, Success weight and BoP (Balance of Performance), are effective.
In this series, we heard from SUPER GT’s Data Inspector (DI), Isamu Komiyama, and Technical Advisor (TAD), Hiroshi Kato, about the success weight rule.

Isamu Komiyama, SUPER GT Data Inspector

Became SUPER GT Data Inspector in 2017 after resigning from a car manufacturer. Komiyama is responsible for collecting and analyzing vehicle data of all cars after qualifying and race and providing it to SRO and GTA. He also chairs the adjustment of performance committee of GTA.

Hiroshi Kato, SUPER GT Technical Advisor

After experiencing various roles at different teams, Kato assumed SUPER GT Technical Advisor in 2024. He is involved in the entire technical domain including the technical part of the sporting regulations, adjustment of performance, etc., and provides support to the technical team. Kato is a member of the adjustment of performance committee.

“2-class mixture” is the core of SUPER GT’s excitement

SUPER GT is composed of two classes, GT500 and GT300, and each class is a separate competition while they run together. “GT” stands for Grand Touring, and “500” and “300” are indications of approximate horsepower, which means race cars with about 500 horsepower and 300 horsepower are competing in GT500 and GT300 classes, respectively, and the first task GTA works on is to adjust the gap in speed between GT500 and GT300 classes.

Having GT500 and GT300 classes run together at the same time ignites battles everywhere on the track, and that is certainly one of the top attractions of SUPER GT.

“We first set a target of how many seconds we want GT300 to be behind GT500, and we achieve the difference in speed that’s required by adjusting BoP mainly on GT300”. (TAD Kato)

This is for enabling GT500 and GT300 cars that run at different speeds to run together safely, and there is no ‘correct’ in determining an ideal lap time difference between GT500 and GT300. It also differs by the characteristics of track layout, and, since both GT500 and GT300 are getting faster and faster, efforts are put so that it wouldn’t be too different from previous years. This is how the ‘2-class mixture’, which is one of the top allurements of SUPER GT and an element that lifts excitement of the race, is realized.

Reason for implementing Success weight and BoP

This year, 15 cars across 3 models and 28 race cars of 13 models of GT500 and GT300 are competing in SUPER GT, respectively. To support such variety of different car models, GTA has implemented the Success weight rule to make it difficult for a same car to produce good results consecutively and sets BoP for every race to equalize the performance of 13 car models of GT300 that have different characteristics.
DI Komiyama and TAD Kato explained about the reason behind the implementation of Success weight and BoP rules.

“If a same car won every time, the race would be boring, wouldn’t it?　Fans want to see the car they support to win, and the race itself would be more fun to watch. That is one of the objectives of implementing the success weight rule”. (DI Komiyama)

“Wide variety of cars are running and battling side by side. That is what the fans think as the fun part and are coming to the circuit for. BoP enables cars with different capabilities to fight on the same battlefield and consequently accomplishes that”. (TAD Kato)

Predefined Success weight and BoP checkpoints are inspected during Official scrutineering and post-race inspection.

Details and objective of Success weight rules

Competed by three different car models, Toyota GR Supra, Nissan Z NISMO, and Honda CIVIC TYPE R-GT, GT500 mandates by the regulations a use of various common parts spanning from monocoque, ECU, clutch, dumper, and brake to even other small parts. Engines are built by the automakers based on the same specification defined by the regulations, in-line 4-cylinder, 2-liter, direct-injection turbocharged engines, therefore, instead of applying BoP, handicap weight, so called Success weight, is imposed to GT500 race cars based on the classifications.
Success weight has a range of 100kg in both GT500 and 300 classes, and the weights are imposed based on

. However, although the weights will be accumulated numerically, the actual ballast mounted on the car is limited to 50kg. For the success weight beyond 50kg, Fuel flow restrictor is used in parallel with ballasts in the GT500 class

which limits the amount of fuel that flows into the engine to forcefully inhibit output (power). On the other hand, the GT300 class has adopted Success refueling restrictor that is used in parallel with ballasts when imposing success weight this season. Diameter of restrictor in the refueling system is changed based on the success refueling restrictor specified. It is intended to increase the time required for refueling to forcefully extend the duration of pit stop. (Diameter of Success refueling restrictor is announced for each race) Application of these handicaps would make it difficult for a same car to continuously finish in an upper position.

Amount of Success weight loaded is indicated by the sticker provided by GTA. Check out side window at back!

Fuel flow restrictor used in GT500. Amount of fuel flowing into engine is adjusted to limit engine power.

＜Table 1＞GT500／GT300｜ Success weight

Until 6th round of participation	7th round	8th round	Maximum success weight
Points x 2kg	Points x 1kg	None	100㎏

・Decimals less than 1kg is rounded up.

＜Table 2＞GT500／Success weight and Fuel flow restrictor

Success weight	０-50㎏	51-67㎏	68-84㎏	85-100㎏
Loaded weight	０-50㎏	34-50㎏	34-50㎏	35-50㎏
Fuel flow restrictor	95.0㎏/h	92.6㎏/h	90.2㎏/h	88.0㎏/h